Drilling Though Wood Core Decks

  • Thread starter George B., s/v Freya
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George B., s/v Freya

I’m looking for some good ideas on how to seal the wood core when I drill some mounting holes through the deck. I’m thinking of drilling a slightly oversized hole, place some tape over the bottom of it and then pouring in wood-penetrating epoxy to the top, letting it cure, and then re-drill the hole. Any other suggestions? How much oversized should the holes be?
 
May 11, 2005
3,431
Seidelman S37 Slidell, La.
Holes in deck

You have the right idea. This is the best way I know of to do this. As to the amount of the oversize, I would think the bigger the better. Make them as big as you can and still cover them with whatever you are installing.
 

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
After you have drilled the holes

and sealed them put a nice wide countersink in the topside so that when you tighten down against the bedding compound some of it is squeezed into the countersink and around the fastener.
 
E

ed

the best way i have found

drill a much larger hole than ;you need. use a tool like an allen wrench to dig out some wood between the laminates. its probably wet anyway, then back fill with epoxy. then drill a new hole thru the epoxy the correct size. put in the calk with the bolt. the core stays dry even if the bolt later leaks.
 
Jul 12, 2004
285
Catalina 320 chestertown
Holes in Deck

And when you are all ready to put it back together, hand tighten, let sit for 24 to 48 hours and then tighten the rest of the way, and don't let the bolt turn.
 
Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
depends on where you are drilling too!

George: It depends on where you are drilling. Some of the boats have aluminum backing plates that are glassed into the deck. In this case you need to drill the correct size hole and tap it for the proper fastener.
 
Oct 25, 2005
735
Catalina 30 Banderas Bay, Mexico
No need to go all the way through ... :)

Here is a method that will make people cringe ... Start by drilling a tap sized hole. Drill through the outer skin and the core, but NOT the other skin. Tap the outer skin for your screw. Use the bent nail / Allen key method to hog out a cavity at least 3 times the screw diameter ( for 1/4-20 that would be 1/4" all around the tapped hole). Spray a screw with Pam or other no-stick cooking spray. Fill the hole with thickened epoxy and screw the non-stick screw into the goo. Let set for 24 hrs. Remove the screw and mount your hardware, no nee for ANY sealant, you have created an epoxy nut inside the deck that is water proof. :)
 
Dec 1, 1999
2,391
Hunter 28.5 Chesapeake Bay
Learning the hard way

Not long ago, I drilled holes in the deck of my H28.5 to mount a few horn cleats on either side. Using the conventional wisdom for this job, I drilled the holes a bit larger than needed in order to tape the underside and fill the holes with epoxy to seal the core. I would then re-drill the holes the right size, fill with caulk and install the cleats. All went well until I poured in the epoxy. What I didn't account for was the space between the inner hull liner and the deck. As a result, I had epoxy dripping out of places below the holes inside the boat. *pop I was lucky to catch this and clean it up before it made a real mess inside the boat. We all keep learning....
 
R

Rich

alternative method

I've avoided doing this method in some locations because I wasn't convinced that the epoxy plug wouldn't pop out or crack away from the balsa core at some point, creating worse leakage potential. An alternative method I used where deck fills went in was to paint a penetrating epoxy paint on the exposed balsa area before putting the fill nozzle back in. it doesn't give the balsa an armor plating but it does give it a good tough coating that will be much better protected than the raw wood if the caulk should give out later.
 
May 18, 2004
259
J-boat 42 conn. river
alternative to the goo

whenever i need to thru bolt anything on the deck, i have an alternative. i gave up on the tube of junk that invariably has dryed out and unusable. i make a gasket out of a material that in the roofing industry is known as epdm. (don't have a freaking idea of what epdm means) basically it is a rubber sheet material that is used on flat commercial roofs. it doesn't deteroriate with uv. after all its used on roofs and expected to last at least 20 to 25 yrs. i just cut a piece with a scissor slightly larger than the shape of what i want to seal, then i can tighten it down completely and trim the excess with a razor knife or sharp utility knife. done, no waiting for it to cure before fully tightening and no messy smears to clean up. i keep a piece of this stuff on the boat at all times. it has been used on the engine also to make a gasket for the heat exchanger and even the water pump. the toughest thing is finding it. only a regular roofing supply house or comercial roofer will have it. home depot or lowes won't have it. BUT once you've found it ,its a god send. i must say though, that its like a model "T" comes in any color you want as long as its black. S/V Que pasa?
 
Jun 4, 2004
629
Sailboat - 48N x 89W
excavate & backfill

EPDM (Ethylene Propylene Diene Monomer) is a synthetic rubber, available in either an uncured (non-vulcanized), or a cured (vulcanized) state. Roofing membranes usually range from thirty mils (0.030") to one-hundred mils (0.100"), with the most common thicknesses being forty-five mils (0.045") and sixty mils (0.060"). The thinner membranes are not really thick enough to perform well as permanent mechanical gaskets. Even a fully watertight rubber gasket does not address the problem of “crushing” a cored sandwich deck assembly, when bolted connections are tightened. The core still needs to be excavated, and backfilled with a compression-resistant material, such as epoxy.
 

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
My boat has a foam core deck

so when it came time to mount hardware I cut out plugs of the deck with a hole saw and epoxyed white oak plugs back in place and glassed over those. I could break a 1/4 inch bolt before I could overtighten and crush the deck. I always counter sink the bolt holes. When the caulk says that it will tolerate 50 percent joint movement and the joint is only .015" thick then .0075" movement will tear the caulk.
 
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